In a wireless communication system, a terminal device wirelessly communicates with other terminal devices through base stations and a core network.
FIG. 1 illustrates a configuration example of a general wireless communication system. Base stations 21 to 24 respectively form cells 210 to 240, which range within a reach of radio waves emitted from the base stations 21 to 24.
A terminal device 11 is located in the area of the cell 210 formed by the base station 21. In addition, the terminal device 11 wirelessly communicates with another terminal device 12 via the base station 21 that is emitting the strongest signals to the terminal device 11. When calling the terminal device 12, the terminal device 11 first transmits a radio frequency (RF) signal to the base station 21. The terminal device 12 is located in the area of the cell 220 formed by the base station 22. The base station 21 routes the RF signal to the base station 22 that is emitting the strongest signals to the terminal device 12 via a core network device 3. Then, the base station 22 transmits the RF signal to the terminal device 12.
Here, when the terminal device 11 moves, for example, the base station emitting the strongest signals to the terminal device 11 may not remain as the base station 21. For example, when the movement of the terminal device 11 causes the cell located within the area of the terminal device 11 to be changed from the cell 210 to the cell 230, the base station 23 becomes the base station emitting the strongest signals to the terminal device 11
Thus, the terminal device 11 searches whether there is a base station that emits stronger signals than the base station 21 with which the terminal device 11 has been communicating previously. This is called scanning. As the result of scanning, when there is a base station that emits stronger signals than the base station with which the terminal device has been communicating previously, the terminal device establishes a communication channel between a newly found base station.
Meanwhile, in the scanning operation, the terminal device receives signals from base stations through a control channel (for example, a broadcast channel) between the terminal device and the base stations. The terminal device then recognizes the identifiers of connectable base stations (CSID: cell station identifier) and the received signal strength indicators (RSSI). The terminal device periodically performs scanning operation except when the communication quality is degraded or the like. Accordingly, the terminal device consumes the battery for scanning.
With regard to this matter, Japanese Patent Application Laid-open Publication No. 2010-81437 discloses that a terminal device determines the necessity of scanning and does not perform unnecessary scanning.
According to Japanese Patent Application Laid-open Publication No. 2010-81437, a displacement amount calculator equipped in a terminal device calculates the displacement amount of the radio communication terminal. When the displacement amount is a predetermined value or less, a scan stopper equipped in the radio communication terminal suppresses scanning of base stations in the vicinity. In the technique of Japanese Patent Application Laid-open Publication No. 2010-81437, a terminal device determines the necessity of scanning and the operation of the determination also consumes power.